Method finish_peek

src/compute-client/src/controller/instance.rs:1991–2004

Fulfills a registered peek and cleans up associated state. As part of this we: Send a `PeekResponse` through the peek's response channel. Emit a `CancelPeek` command to instruct replicas to stop spending resources on this peek, and to allow the `ComputeCommandHistory` to reduce away the corresponding `Peek` command. Remove the read hold for this peek, unblocking compaction that might have waited

(&mut self, uuid: Uuid, response: PeekResponse)

    ///    command.
    ///  * Remove the read hold for this peek, unblocking compaction that might have waited on it.
    fn finish_peek(&mut self, uuid: Uuid, response: PeekResponse) {
        let Some(peek) = self.peeks.remove(&uuid) else {
            return;
        };

        // The recipient might not be interested in the peek response anymore, which is fine.
        let _ = peek.peek_response_tx.send(response);

        // NOTE: We need to send the `CancelPeek` command _before_ we release the peek's read hold
        // (by dropping it), to avoid the edge case that caused database-issues#4812.
        self.send(ComputeCommand::CancelPeek { uuid });

        drop(peek.read_hold);
    }

    /// Handles a response from a replica. Replica IDs are re-used across replica restarts, so we
    /// use the replica epoch to drop stale responses.